Degree

Doctor of Philosophy (PhD)

Department

Entomology

Document Type

Dissertation

Abstract

The fall armyworm, Spodoptera frugiperda (J.E. Smith), is a target pest of Bacillus thuringiensis (Bt) crops in North and South America. However, after more than two decades of the intense use of Bt crop technology, S. frugiperda has developed resistance to Bt corn in several countries. The objectives of this study were: 1) to characterize the inheritance and fitness costs of Cry1A.105 resistance in S. frugiperda; 2) to evaluate larval survival and plant injury of Cry1A.105-susceptibile, -resistant, and -heterozygous S. frugiperda populations on transgenic corn plants containing single or pyramided Bt genes; 3) to estimate the frequency of Cry2Ab2 resistance alleles in field populations of S. frugiperda in the U.S. southern region; and 4) to evaluate the phenotypic performance of different genotypes of S. frugiperda possessing single- or dual-Cry1A.105/Cry2Ab2 resistant genes on MON 89034 corn. Cry1A.105 and Cry2Ab2 are the two Bt proteins expressed in the Bt corn event MON 89034, a common Bt corn trait. The results showed that Cry1A.105 resistance in S. frugiperda was inherited as a single autosomal and non-recessive gene with no fitness costs. Three commonly planted pyramided Bt corn traits (Genuity® VT Double ProTM, SmartStaxTM, and Agrisure® VipteraTM 3111) were highly effective against the Cry1A.105-resistant S. frugiperda. Frequency of major Cry2Ab2 resistance alleles in field S. frugiperda populations was estimated to be 0.0023 in the U.S. southern region. One F2 family from Georgia was confirmed to possess a major resistance allele to Cry2Ab2. A Cry1A.105/Cry2Ab2 dual-gene resistant S. frugiperda strain was generated by crossing the Cry1A.105-resistant and Cry2Ab2-resistant strains. Insect survival, growth, development, pupation, and reproduction of nine genotypes of S. frugiperda possessing Cry1A.105/Cry2Ab2 resistant alleles were evaluated on leaf tissue and whole plants of MON 89034. The nine insect genotypes were a Cry1A.105/Cry2Ab2-susceptible (aabb), a Cry1A.105 resistant/Cry2Ab2-susceptible (AAbb), a Cry1A.105-susceptible/Cry2Ab2-resistant (aaBB), a Cry1A.105/Cry2Ab2-resistant (AABB), and five heterozygous (AaBb, AABb, AaBB, Aabb, aaBb) genotypes that were produced from various crosses among aabb, AAbb, aaBB, and AABB. Laboratory bioassays and greenhouse tests exhibited that AABB was highly resistant to MON 89034. Genotypes containing one or two resistance alleles were overall susceptible to MON 89034, while those possessing three resistance alleles exhibited a significant level of resistant to the Bt plants. Information generated from this study should be valuable in assessing resistance risk, refining resistance management modeling, and developing resistance management strategies for the sustainable use of the Bt corn technology.

Date

6-29-2018

Committee Chair

Huang, Fangneng

Included in

Entomology Commons

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